Various metals can be recovered from their ores by leaching. Leaching is accomplished by contacting ore-containing rock with an aqueous acidic solution. A metal of choice can be obtained from a body of ore which contains a mixture of metals in addition to the desired metal. The leaching medium dissolves salts of the desired metal and other metals as it trickles through the ore, to provide an aqueous solution of the mixture of metal values. The metal values are usually leached with a sulfuric acid medium, providing an acidic aqueous solution, but can also be leached by ammonia to provide a basic aqueous solution.
The aqueous leaching solution is mixed in tanks with an extraction reagent which is dissolved in an organic solvent, e.g., a kerosene. The reagent includes an extractant chemical which forms a metal-extractant complex with the desired metal ions in preference to ions of other metals. The step of forming the complex is called the extraction or loading stage of the solvent extraction process. The nature of the extractant depends upon the metal to be extracted and the nature of the leach solution. For example, zinc can be extracted with di-2-ethylhexylphosphoric acid, uranium using a tertiary fatty amine reagent such as ALAMINE® tertiary amine, cobalt as the chloride complex using a tertiary fatty amine reagent such as ALAMINE® tertiary amine, cobalt using an organo phosphonic acid or phosphinic acid, nickel using a carboxylic acid, molybdenum using a tertiary fatty amine reagent such as ALAMINE® tertiary amine. Copper can be extracted with an aldoxime such as 2-hydroxy-5-nonyl benzaldoxime, a ketoxime such as a 2-hydroxy-5-alkylphenyl ketoxime or combinations of aldoximes and ketoximes such as is described in U.S. Pat. No. 6,395,062, the entire contents of which are incorporated herein by reference and oximes in combinations with extractant and equilibrium modifiers such as is described in U.S. Pat. Nos. 6,231,784 and 6,177,055, the entire contents of each of which are incorporated herein by reference.
New and more economical methods of improving the extraction process are continuously being sought in order to lower costs and improve the quality of the metal produced.